Conventional lumber lug loaders have been refined over the years so as to operate quite adequately in basic situations, but are found to be inadequate when it comes to higher speeds and are not very versatile in the singulating and feeding of lumber of varying width and height, into lug spaces. There are fewer problems encountered when handling lumber that has been planed, which is uniform in width and height, but when the lumber being handled is of varying widths and varying in thickness, or bowed (as may be more predominant in modem curve sawing mills), cupped or crooked, it becomes increasingly difficult to handle the lumber at acceptable speeds. There have been some attempts at solving these problems in the past, but these devices are usually limited in their success when the lumber being stacked is not uniform in size and shape, and when the stacking speeds are increased.
An example of a lug loader is U.S. Pat. No. 3,923,142 issued to Rysti in 1975, for a Method and Apparatus for Dosage of Sawn Timber. Although this system is somewhat successful at delivering lumber to a lugged transfer, its design is questionable when it comes to handling varying widths and thickness, as well this design was never very successful in the industry.
Applicant is also aware of U.S. Pat. No. 5,518,106 issued to Allard in 1996, for an Apparatus for Separating and Individually Feeding Boards and Cants to a Processing Unit. The Allard device uses a fixed heel on the rotating discs, that have a tendency to mark the underside of the board as it is released. The device also requires a speed up belt to pull the board away from the fixed heel at the top of the disc to prevent deep marking of the board and to prevent the board from being flipped. In some mills the boards have been marked for trimming etc. before the lug loader, and if the board has been flipped (as does happen some times with the Allard device even with a speed up belt) then the board has to be flipped back to read the mark, which can be difficult in a high speed feeding situation.
The speed up belt at the top of the rotating disc causes the out feed to have to change elevation, which can be expensive, and which takes up more floor space which may not be available in a retrofit situation. If a board is planned or is destine for cabinet making etc. then any marks from the heel will reduce the value of the board.